1. Field of the Invention
The present invention relates to a tractor with a front suspension and particularly to a tractor where the front suspension components are mounted directly to a mechanical front wheel drive differential case.
2. Description of Related Art
To improve tractor performance, front axle suspension systems are becoming more commonplace. A front suspension provides improved operator comfort, thereby reducing operator fatigue. In addition, the tractor frame is subjected to less impact loading during operation. A front suspension axle, however, adds complexity and additional components to the front axle.
To further improve the performance of agricultural tractors, many tractors are provided with mechanical front wheel drive. While the front wheels and tires are typically smaller than the rear, by driving both the rear and the front wheels, tractive efficiency is improved. A mechanical front wheel drive requires a front drive axle with considerably more components compared to a front axle without front wheel drive.
Many competing design requirements make it difficult to package front wheel drive and a front axle suspension in a tractor. These design requirements include: ground visibility over the hood; high crop clearance; and a small turning radius. These requirements place a premium on space at the front axle, especially with front wheel drive and a front wheel suspension.
The tractor of the present invention overcomes the packaging difficulties described above by integrating the engine oil pan into the mechanical front wheel drive differential case and by integrating the suspension mounting bosses into the differential case casting. The integration of the oil pan into the differential case eliminates the need for a separate oil pan and the vertical packaging space needed for the pan. This enables both the crop clearance and the front ground visibility over the hood to be improved.
The differential case itself is an integral part of the tractor frame. There are no frame members extending longitudinally of the tractor along side or beneath the engine. The differential case is the frame. While the engine oil pan has previously been integrated into the tractor frame, the front drive axle has been a beam structure in which the front differential is part of a pivoting axle beam. This front beam axle is pivotally mounted to the frame about a longitudinal axis but it is not suspended from the frame.
The integration of the suspension mounting bosses into the differential case casting reduces the number of components needed to attach the suspension system control arms to the vehicle structure, in this instance, the differential case. By eliminating components, more space is available for the suspension arms, the drive shaft, the steering cylinder and tie rods.
The suspension system is an independent suspension having upper and lower control arms on each side of the differential case extending outward to steering knuckles that support final drive assemblies. The left and right sides of the suspension system are mechanically independent from one another. The left and right sides are coupled through a common gas accumulator providing fluid pressure to hydraulic cylinders on each side of the suspension.
A steering cylinder is also carried by the differential case having a cylinder rod extending from both sides of the differential case to which tie rods are attached and extend to the steering knuckles. The upper control arm has an inboard end attached to a mounting boss projecting laterally outward from the differential case. The inboard end of the upper control arm is:forked, having two spaced apart legs that are placed on opposite sides of the mounting boss. A single pivot pin extends through both legs of the upper control arm and through the mounting boss to pivotally attach the upper control arm to the differential case. The lower control arm has two separate attachments to the differential case. A forward branch of the control arm is forked, like the upper control arm, and has a pivot pin extending through the two spaced legs of the fork and through a mounting boss extending laterally from the differential case. The rear branch of a lower control arm has a rear pivot pin extending therethrough that is bolted directly to the side of the differential case. No separate mounting brackets are attached to the differential case for attachment to the control arms.
In addition to the control arms, the suspension includes a hydraulic cylinder that functions as a spring. The hydraulic cylinder is bolted to a mounting boss on the differential case at one end and has an extending rod that is bolted to the lower control arm to carry the suspended tractor mass. By integrating the suspension attachments into the differential case, fewer components are required for the suspension, thus providing the designer with greater flexibility in locating axle components. In addition, greater visibility through the axle to the ground between the tires and the tractor hood is obtained.